This invention relates to a diopter-adjusting device for use in a finder-interchangeable type single reflex camera.
Various types of cameras incorporating the diopter-adjusting devices are known. However, these cameras generally suffer from the shortcoming that an operating member for adjusting a diopter is exposed to the exterior of the camera so that there is a danger of the operating member being operated inadvertently. To cope with this, it has been proposed to incorporate a locking means in the operating member to prevent the aforenoted inadvertent operation. However, the diopter adjustment is not operated as often as, for example, the focus adjustment for an objective lens, so that it is preferable that the diopter-adjusting-operating member be positioned in a concealed condition from the exterior of a camera.
With the interchangeable-finder type single lens reflex camera, wherein a finder is mounted on the body of the camera, if the diopter-adjusting-operating member is positioned so as to be concealed from the exterior of a camera then there is no danger of hands or other objects contacting the diopter-adjusting-operating member upon taking a picture or handling of the camera, thereby precluding a variation in the diopter or dioptic power.
Meanwhile, the interchangeable-finder type single lens reflex cameras are no exception to the general rule that many parts should be positioned in a small space in a camera body. Thus, the sizes of respective parts are designed to be as small as possible without impairing their functions. This is also true with an eyepiece and, therefore, the portion of the eyepiece lens through which light is not transmitted is cut away so that the configuration of the eyepiece is not cylindrical but rectangular. It has been a general practice to adopt a helicoid i.e., the rotating movement moving the eyepiece back and forth along the optical axis, for the purpose of adjusting the diopter. To this end, however, the configuration of the eyepiece should be cylindrical, resulting in an increase in size of an optical system. This may be a considerable sacrifice for a camera in which the reduction in size thereof is one of the important requirements.